The Time domain reflectometry have been for many years and remain the fastest and most accurate instruments for detecting the structural problems of wiring. TDRs are used to locate and identify faults on any type of twisted cables and coaxial cables.
The uses of TDR are as follows:
Locate faulty fittings.
Locate unknown splices.
Find components on the line.
Locate water or moisture in the cable.
Assistance in the measurement and verification of new cable reels.
Locate holes or damage to the cables.
To document the integrity of the wiring.
To document or map wired networks.
Principles of Operation
The TDR works with the same radar principle. A pulse of energy is transmitted through the wire to be tested, and when the pulse reaches the end of the wire, or a fault along this, part or all of the pulse energy is reflected towards the instrument.
The TDR measures the time it takes for the signal to travel on the cable, between the instant the signal was sent and the instant it received the signal reflected by the point of discontinuity, this time converts it to a distance and shows the magnitude of discontinuity.
TDR analysis generally does not detect capacity isolated devices or inductive. In such cases the TDR scan is complemented by a detailed high frequency evaluation and a physical inspection.
Impedance
The TDR identifies changes in cable impedance that may be caused by a variety of circumstances, including cable damage, water ingress, changes in cable type, improper installation, and any manufacturing defects.
The insulation material that holds the conductors apart is called dielectric and the impedance of the wire is determined by the spacing between the conductors and the type of dielectric used.
The reflection of the pulse sent by the TDR to the cable, is produced by a change of Impedance along the cable and these changes are what determine the amplitude of the reflection.
The Width of the Pulse
Many TDRs have selectable pulse widths, and the higher the pulse, the more energy is transmitted to the wire. The pulse widths used are: 2 ns, 10 ns, 100 ns, 1000 ns, 2000 ns, and 4000 ns. According to the TDR model you can include all or just a few pulse widths.
If the fault is very small, the energy of a small pulse may not be enough to travel through the wire, see the fault and that the reflected pulse travel back, this added to the attenuation of the wire, can cause the detection of this fault becomes a bit difficult. In this case the energy should be increased so that the fault can be appreciated.
Las formas de onda de los pulsos mostrados en las figuras muestran los cambios en estas, al solo cambiar el ancho del pulso (con el mismo cable y las mismas configuraciones del TDR).
The need to know the salinity of the hydrocarbons is due to the fact that this salinity indicates many characteristics and properties of the hydrocarbon such as: its origin related to the salinity of the associated congenital water, the connectivity of the different wells in a field, the effects of the Salinity in the viscosity and fluidity of the hydrocarbon, the variation of the salinity by the physical and chemical changes of the hydrocarbon when varying the pressure and the temperature, the invasion of aquifers of fresh or salt water towards the well, among others. This information is very important for well completion in order to improve and optimize production. In addition to the need to incorporate reserves, there is the cost of high oil prices, which motivate the application of new technologies for improved recovery of hydrocarbons. Within these technologies is the improved recovery process by injection of thermal fluids mixed with catalysts to promote an in situ reaction. Pemex Exploration and Production currently documents these types of tests to be applied in offshore and offshore fields (fractured carbonate sites).
The TDR technique has been widely used to detect faults in electrical transport cabling systems, computer network systems and electronic telecommunication systems. Research is currently underway to apply this technology in the detection of leaks in tanks and pipelines, for application in industry and to determine soil moisture, for application in agriculture (nurseries and fields). In these cases it is not required to have as much accuracy of the return signal to determine the location and magnitude of the fault that is normally a short circuit or an open circuit. However, to perform the measurement of some variable (such as salinity) by the TDR method, a high accuracy is required in the equipment that records the return signal, which in this case is the oscilloscope, not only to detect the presence Of salt in the fluid, but to quantify the amount of salt and to make a reliable measurement.
However, because of the accuracy required to quantify the TDR return signal, this technology has not been commercially applied under standard conditions to ambient temperature and pressure, much less to downhole conditions.
Doing a patent search that could be related to our invention, we find the following:
The U.S. Pat. No. 6,114,857A dated Sep. 5, 2000, entitled “System and Method for Monitoring Corrosion in Oilfield Wells and Pipeline Utilizing Time Domain Reflectometry”. A system for measuring and controlling corrosion in oil well production pipelines at well bottom conditions is described.
In our invention, although the conditions of pressure and temperature at the bottom of the well could be similar, the objective and operation of the system are completely different, both in the conditions of the signal sent by the signal generator, and in the form and interpretation of the response signal. In this case the corrosion is measured and in our case salinity is measured that have completely different behaviors.
The U.S. Pat. No. 8,912,806B2 dated Dec. 16, 2014, entitled “Method of Cutting and Testing a Pipeline Cut Under Water or Under Seabed”. A system based on Time Domain Reflectometry (TDR) is described, It can be determined when a pipe has been cut completely when work is done deep well or on the seabed. In this technology, electromagnetic signals are sent through the pipeline and returned to the TDR signal analyzer. These signals are different when the pipe is complete and when it is broken.
As can be seen, the aim of this invention and the present invention is completely different, as are the signals and the interpretation thereof.
The patent US20040100273A1, entitled “Testing Electrical Integrity of Electrically Heated Subsea Pipelines”, refers to a method where electrical connectivity is tested by Time Domain Reflectometry (TDR) of a heating system of the pipes coming from the Wells and cross the seabed to the surface. This heating of the pipes is required to prevent thermal shocks or cooling of the oil as it passes through the seabed.
This application differs from our invention in that, in this case, the TDR system only verifies the connectivity of the system to avoid open circuits or short circuits that affect the operation of the heating system, using the same pipe as a waveguide. In our case, the response signal in the TDR should not only identify a change in impedance but also quantify it to determine the salinity of the oil at the bottom of the well.
The patent US20140085133A1, entitled “Time Domain Reflectometry Based Method for Emulsion Detection and Profiling”, relates to a method by which the presence and location of an emulsion at an interface which may be liquid and gas (water and air) or Two non-miscible liquids (water and oil), in this way the level of liquid in a tank can be measured.
The difference with our invention is that these tests to determine the location of the emulsions are carried out under conditions of pressure and ambient temperature, however, in our invention, the test conditions are well bottomed.